Combobox need Two Tabkeys in IE7

package lu.repondo.common.pojo;

public class Currency {
	Integer currencyid = new Integer(-1);
	String iso4217 = "";
	
	public Integer getCurrencyid() {
		return currencyid;
	}
	public void setCurrencyid(Integer currencyid) {
		this.currencyid = currencyid;
	}
	public String getIso4217() {
		return iso4217;
	}
	public void setIso4217(String iso4217) {
		this.iso4217 = iso4217;
	}
}

<?page title="new page title" contentType="text/html;charset=UTF-8"?>
<zk>
<zscript language="Java"><![CDATA[                               
	import lu.repondo.common.pojo.Currency;
	
	List waehrungen = new ArrayList();
	Currency c= new Currency();
	c.setCurrencyid(new Integer(1));
	c.setIso4217("EUR");
	waehrungen.add(c);
	
	c= new Currency();
	c.setCurrencyid(new Integer(2));
	c.setIso4217("USD");
	waehrungen.add(c);
]]>
</zscript>

<window title="new page title" border="normal">
	<label value="insert 1 or 2: " />
	<textbox id="a" onBlur="setCombo()"/>
	<textbox id="b" />
	<combobox width="116px" id="cmbCurrency" mold="rounded" >
		<comboitem forEach="${waehrungen}" label="${each.iso4217}" value="${each.currencyid}"/>
	</combobox>	
	<textbox id="c" />

<zscript language="Java"><![CDATA[                               
	public void setCombo(){
  			Integer nWaehrung = new Integer(a.getText());
  			for(int i=0;i<cmbCurrency.getItemCount();i++){
  				Integer nKey = (Integer)cmbCurrency.getItemAtIndex(i).getValue();  				
  				if (nKey.intValue() == nWaehrung.intValue()  ){
  					cmbCurrency.setSelectedIndex(i);
  					break;
  				}
  			}		
  	}
	
	a.setFocus(true);	
]]>
</zscript>
</window>
</zk>